1. Technical Field of the Invention
The invention relates to the domain of manufacturing of electronic chips and particularly the operating tests phase.
More precisely, the invention relates to the manufacturing stage during which chips are created on wafers, usually silicon wafers that are circular lamellas cut from a semiconducting material on which up to several thousand chips are manufactured simultaneously and are subsequently separated.
2. Description of Related Art
The chips are integrated in more and more products in daily life (general public) and for professional purposes. The development of optical products such as webcams, portable photo cell phones or 3G phones, optical mice, etc., requires integration of photosensitive chips in these electronic devices.
The invention is specifically applicable to manufacturing of these photosensitive chips.
Before each chip can be integrated into a corresponding package, its operation has to be tested both electrically and optically, in other words its electrical operation under given illumination conditions.
Electrical and optical test devices for chips are known in prior art.
Such test devices are described in more detail later on (see, FIGS. 1A and 1B), and conventionally include a prober coupled to a probe card (needle card) on which a wafer is mounted containing the chip(s) to be tested. There is another block above this block corresponding to a test head. The needle card is a printed circuit board (PCB). It is used to test operation of the chips by contact between the electrical connection means (the needles) and determined pads on the chips to be tested.
For test devices concerning photosensitive chips, the needle card is perforated to allow light to pass through the card, either directly through the holes or along guides, for example optical fibers.
The light test checks the electronic behavior of photosensitive chips under the influence of a chosen light, representative of the operational usage conditions of the finished product containing the chip(s) in question. For use under realistic conditions, the test is used to detect chip response defects, and therefore to make a selection and chips that do not satisfy determined quality criteria are eliminated.
The tests are done chip by chip in series, or in parallel, depending on the number of chips on the wafer, and their complexity (number of pads per chip). In terms of productivity, it is desirable to perform the tests in parallel.
Production of light and checking of illumination conditions are essential. The test must be capable of varying these illumination conditions, for example by the number of lux per unit area, the wavelength, the lighting frequency, the signal/noise ratio, etc. The order of magnitude of specifications for a given chip type can then vary up to several hundred.
Furthermore, there is a computer test program and an expected behavior model of the chip. The real behavior should be compared with the expected behavior and the tested chip may or may not be retained for the remainder of manufacturing, depending on differences in behavior and given quality criteria.
Known solutions use light sources on the input side of the probe card, either inside or outside the test head, that illuminate the wafer with a particularly complex opto-mechanical system. Furthermore, in order to carry out tests in parallel, the illuminators must obtain good light quality uniformity over a large area, which is particularly difficult to achieve.
In order to enable tests of photosensitive chips, a conventional illuminator has a complex structure including particularly an external energy source, an illumination controller, a closer, color filters, opto-mechanical attenuators, lenses and a light source.
This configuration creates a number of problems including that a test device, due to its complexity, is dedicated to a given type of chip test, which reduces the flexibility of the production line.
Furthermore, due to the complexity and the manner in which light is brought to the outside surface of the wafer through an optical fiber or a particular arrangement of lenses, a large quantity of light energy is necessary at the source. Such energies are usually produced by halogen lamps that have a limited life and for which optical properties are neither uniform nor stable in time. Furthermore, if the light source is outside the test head, the size inherent to such a source is also a problem.
It is difficult to obtain uniform light distribution at the wafers for tests in parallel, which requires increased complexity in the arrangement of lenses and requires even higher power at the source.
If a light source is placed outside the test head (halogen source), such a configuration makes it impossible to use strobe light, however this is necessary for changing light conditions during the test, for example for tests related to integrated chips in optical mice.
Finally, since probe cards are perforated, wiring in these probe cards is relatively complex because the optical path must be free, therefore there must be no optical or electrical cable located on this optical path.
Thus, having seen the complexity of test devices and specific features of illumination conditions, testers are dedicated to a specific type of chip. This causes problems in production lines, if only due to the time necessary to change the means useful for production for a given illumination condition.
The purpose of this invention is to overcome these disadvantages by proposing a probe card for electrical operating tests of at least one chip provided with connection pads under illumination conditions given by a lighting means, said probe card being a printed circuit board (PCB) including electrical connection means to said chip on its lower face.